The third generation of communication system (3G) with code division multiple access (CDMA) technique, in which multimedia services is well supported, will be highly competitive for several years. However, in order to ensure competitiveness in a longer time, the 3GPP starts the research project of long-term evolution (LTE) of 3G radio-access technology. The main targets of LTE project are reduction of the time delay, enhancement of user data rate, improvement of the capacity and the coverage, and reduction of the operator's cost.
According to the progression of the research, two types of frame structures are supported: Generic frame structure and Alternative frame structure. The Generic frame structure supports both frequency division duplex (FDD) and TDD systems; and the Alternative frame structure supports TDD systems only.
The Generic frame structure is shown in FIG. 1: one 10 ms length radio frame consists of 20 time slots (TS), indexed from #0 to #19, each TS length is 0.5 ms, and a subframe is defined as two contiguous TS.
The Alternative frame structure is shown in FIG. 2: a 10 ms length radio frame is divided into two 5 ms half-frames, each half-frame consists of 7 service time slots TS0˜TS6, which correspond to #0 to #6 in FIG. 2, and three special time slots DwPTS, UpPTS, and GP. One service time slot is also called a Transmission Time Interval (TTI) or a sub-frame, an UL/DL switch-point is set between TS3 (#3) and TS4 (#4) as shown in FIG. 2. The service time slot is used for data and control signaling transmission, the downlink special time slot (DwPTS) is used for transmitting downlink synchronization information of the system, the uplink pilot time slot (UpPTS) is used for uplink random accessing, and the switch protection time slot (GP) is used for providing time interval, during which the downlink transmission time slot is switched to the uplink transmission time slot.
The length of TTI of LTE TDD is a length of a service time slot, viz. 0.675 ms. A service time slot is consisted of 9 or 8 orthogonal frequency division multiplexing (OFDM) symbols, which respectively correspond to cyclic prefixes (CP) of different lengths. FIG. 3 provides a structure of the service time slot in the case of short CP: a service time slot is consisted of 2 short blocks (SB) and 8 long blocks (LB), SB is usually used for transmitting a reference symbol (or called “pilot symbol”), such assignation can reduce the resource used by the reference symbol. Each service time slot can be used for uplink or downlink data transmission, generally a structure in which each half-frame has only one UL/DL switch-point is adopted, and the uplink-to-downlink data transmission ratio can be adjusted flexibly by adjusting the position of the UL/DL switch-point, in order to meet different application requirements.
Among the three international standards of 3G, TD-SCDMA is the only one that supports TDD. TD-SCDMA can be flexibly assigned to match the asymmetric uplink and downlink service. And with the advanced wireless communication technologies, such as smart antenna, uplink synchronization, joint detection, and software radio etc., the TD-SCDMA system can achieve comparative high performance and spectrum efficiency. In order to keep the competitiveness of TD-SCDMA system for a long term, the TD-SCDMA system needs to continuously develop and improve the performance as well. In the long-term evolution projection LTE TDD of TD-SCDMA, the alternative frame structure is highly preferred for the compatibility with the TD-SCDMA system as shown in FIG. 2.
In the modern digital communication system, the design of control signaling has large influence on the performance of the system. The uplink control signaling can be divided into two kinds: data associated control signaling and non-data associated control signaling. The data associated control signaling is the information used for processing uplink package, such as the modulation/coding scheme (MCS), new data indication (NDI), multi-antenna mode (MIMO mode) etc. The non-data associated control signaling mainly includes downlink channel quality indication (CQI) for scheduling or link adaptation and acknowledge (ACK) of the downlink package etc.
For LTE system, including both LTE FDD and LTE TDD, since the system transmission parameters are determined by NodeB, i.e. the user equipment (UE) transmits the uplink data based on the parameter indicated by downlink control signaling from the NodeB, so only the non-data associated control signaling needs to be transmitted. The uplink control signaling of LTE TDD mainly includes downlink channel quality indication (CQI) and acknowledges signal (ACK/NACK), and the LTE FDD system further needs to transmit codebook information of pre-coding matrix.
The agreed basic transmission characteristics of the uplink control signaling for both LTE FDD and LTE TDD are:    1) the control signaling and data are multiplexed before operation of Discrete Fourier Transform (DFT), when UE transmits data and control signaling simultaneously;    2) the control signaling is transmitted on the reserved frequency resource, when UE only need uplink-transmit uplink control signaling.
The key for realizing the above mentioned transmission solution of uplink control signaling is to design the control channel without uplink data transmission.
A relative concrete designing solution of control channel without uplink data of LTE FDD is shown in FIG. 4, wherein the lateral direction represents frequency domain (Frequency), the longitudinal direction represents time domain (Time), 1 indicates frequency-hop sequence 1, 2 indicates frequency-hop sequence 2, 3 indicates frequency-hop sequence 3, 4 indicates frequency-hop sequence 4, 5 indicates data, and 6 indicates non-data associated signaling transmitted together with the data 5. The frequency-hop sequence 1, frequency-hop sequence 2, frequency-hop sequence 3, and frequency-hop sequence 4 are non-data associated control signaling individually transmitted. An uplink control signaling dedicated frequency resource of fixed size is reserved in each uplink time slot, the individually transmitted non-data associated control signaling is transmitted in the reserved area at both sides of the frequency domain by a frequency hopping way. Since each sub-frame reserves frequency resource for uplink control signaling transmission, the control signaling can obtain diversities in time and frequency simultaneously, so that the reliability of the control signaling is improved.
For LTE TDD, there is still no feasible solution for the control channel without uplink data.
The difference between TDD duplex mode and FDD duplex mode causes the transmission mode of control signaling in TDD system to be different from that in FDD system, particularly shown as the followings:
First, since the Alternative frame structure adopted in TDD system has a time division structure, in which the uplink-to-downlink time slot ratio is variable, this renders: 1) change of the total amount of the uplink control signaling; 2) change of available uplink resource. Hence, if the LTE FDD solution shown in FIG. 3 is adopted, each uplink time slot reserves uplink control signaling dedicated frequency resource of fixed size, which will render resource waste.
Second, in Generic frame structure, a sub-frame is consisted of two time slots, which can easily improve the performance of the control channel by frequency hopping in units of time slots; however, in Alternative frame structure, each sub-frame is consisted of one service time slot, so each sub-frame has to be divided to realize frequency hopping.
Third, according to the control signaling, TDD is also distinguished from FDD. For instance, FDD system adopts codebook based pre-coding, wherein the uplink control signaling needs to feedback codebook index, while TDD system adopts non-codebook based pre-coding, and does not need to feedback associated pre-coding matrix information. This will be reflected on the difference of the number of the uplink control signaling and of the resource used by the uplink control channels.
Owing to the above, with the development of the present LTE standard, the uplink control signaling of FDD duplex mode preferably transmitted in each sub-frame (1 ms) consisted of two time slots. When the user needs to transmit uplink data and control signaling, the control signaling and data are multiplexed before DFT; when the user only transmits control signaling, the control signaling is transmitted on the reserved frequency resource. For the LTE TDD system adopting Alternative frame structure compatible with TD-SCDMA, the uplink control channel has to be designed in consideration of its frame structure and duplex characteristics, so as to ensure the reliability of control signaling, save resource, perform flexible assignation and so on. However, at present, there is no solution for uplink control channel transmission in consideration of the characteristics of LTE TDD system, i.e., there is no feasible solution of the control channel without uplink data.